Photovoltaics: How we do it – and why

SolarWorld. And EveryDay is a SunDay www.solarworld-usa.com RETURNNING TO THE SUN

“Environmental ills and climate ENERGY CRISIS LIFE’S POWER PLANT change pose glo- Over the past two centuries, humans learned Perpetually renewing power from the sun has to harness fossil fuels on a vast scale to power fueled life on Earth since its first spark. bal crises for our an industrial revolution. This quantum advance From cellular to mammalian in machine automation, mass production and planet. Any answer forms, the sun has supplied a labor division drove unparalleled improvements critical ingredient in the recipe to these problems in the health, economics and comforts of citi- for living beings. More practi- zens of industrialized nations. must be powerful. cally, humans have relied on Fortunately, we But today, the solar power – to warm water, dry benefits come at clothes and prepare food – as far need only tap the great, unpaid as history’s record reaches. environmental The sun emits so much energy that solar power source of costs. Fossil fuels experts compete to put the output in terms cannot continue to be life’s history for an- we can grasp. Here’s just one: Earth receives humanity’s primary enough solar radiation in an hour to supply the swers: the sun and source of energy. planet’s electrical needs for a year. its ample energy.” It’s time for an energy foundation in harmony with the planet. It’s time for a solar revolution. Frank H. Asbeck SolarWorld chairman and CEO PV POINTER

Of the 92 elements, silicon (Si) is the Earth’s most prevalent semiconductor – and second most common element of any kind, after oxygen. Appearing in silicon oxides such as sand (silica), quartz, rock crystal, amethyst, agate, flint, jasper LIFE’S POWER PLANT GATHERING THE SUN’S BOUNTY and opal, silicon makes up about a quarter, by weight, of Now people are re-tapping their roots in a solar world by using panels of the Earth’s crust. Photovoltaic photovoltaic (PV) cells to generate power from the sun’s rays. manufacturing starts with As reliable as the sun itself, the technology is simple and clean. Cells are built polysilicon, a refinement of silicon materials. on wafers of silicon made from ordinary sand and quartz. Assembled into modules and exposed to the sun, the cells directly convert light into electricity – without polluting emissions, resource depletion or moving parts. SolarWorld, extraordinary because it undertakes all phases of PV manufac- WORD TO KNOW turing and makes no other products, builds modules in four steps, starting with sand and ending with sun. Photon: A photon is neither Turn the page to begin the story behind SolarWorld’s core mission to put the a wave nor a particle, but technology to work for homes and businesses around the world. instead a packet of light energy. Solar radiation arrives on the surface of photo- voltaic cells in the form of photons, providing the main energy that activates cells to produce electricity. ROOTS OF A RENEWABLE

The history of 1954 Bell Labs announces 1960 Hoffman Electronics invention of the first modern creates a 14%-efficient solar cell. the solar industry silicon solar cells, with energy- conversion efficiency of about 6 1961 United Nations stages and SolarWorld “Solar Energy in the Developing 1973 Solar cells power percent. Skylab, the first U.S. space are intermixed, World” conference. 1955 Western Electric licences station. each with one commercial solar cell 1962 The Telstar communica- technologies. tions satellite is powered by 1974 A home in New foot squarely solar cells. Mexico is the world’s positioned in the 1957 AT&T employees Gerald first to be powered L. Pearson, Daryl M. Chapin and 1963 Viable photovoltaic only by solar and United States Calvin S. Fuller receive patent module is produced out of wind energy. silicon solar cells. and the other in US2780765, “Solar Energy Converting Apparatus.” 1977 Engineer and entre- Germany – the 1964 Yale preneur Bill Yerkes sells two markets that 1958 Hoffman University startup Solar Technology Electronics- Press publishes International to Atlantic have led the in- Semiconductor Division Farrington Richfield Co., forming ARCO Solar. dustry’s develop- creates 9%-efficient Daniels’ landmark solar cells. book, “Direct Use of the Sun’s 1979 In Camarillo, Calif., ment. In the U.S., Vanguard 1, the first Energy.” ARCO Solar dedicates world’s SolarWorld began solar-powered satellite, largest PV factory to making is launched with .1 watt as ARCO Solar. silicon crystal ingots, wafers, solar panel. photovoltaic cells and Siemens and Shell 1967 Soyuz 1 becomes first modules. manned spacecraft using solar. then owned the World annual PV unit before Solar- array production World bought it. MWp 1950s 1960s 1970s 10,000 PV POINTER

Pioneering relativity theorist Albert Einstein won the Nobel Prize in 1921 – but not for his ROOTS OF A RENEWABLE renowned relativity equa- tion E=mc2. The prize actually 1990 Siemens acquires celebrated his 1905 discovery ARCO Solar, forming of exactly how light caused 1,000 what was then called the Siemens Solar. photoelectric effect – essen- tially, photovoltaics. Today, SolarWorld issues its annual 2002 Royal Dutch Einstein Awards to honor PV 1996 Siemens Solar cele- Shell acquires Siemens researchers. brates 100 MW of installed Solar, creating Shell Solar. power from modules made in Camarillo. 2006 SolarWorld aquires Shell Solar. 100 1980 ARCO Solar becomes 2007 Investors begin first company to produce offering free installation more than 1 megawatt in return for long-term of PV modules in 1997 Siemens becomes first power purchase agree- one year. company to offer 25-year ments (PPAs), which be- warranty. come common financing arrangements. 1998 Solar- 1982 ARCO Solar commissions world’s World forms as ORD TO NOW startup business, 2008 Solar- W K first 1 MW grid-con- World opens 10 nected PV installation. entering Germa- ny’s burgeoning 480,000- solar market. square-foot Photovoltaic. The word 1985 Australia’s University plant in photovoltaic comes from the of New South Wales creates 1999 Germany Hillsboro, words photo, meaning light, silicon cells with 20% ef- investing $500 million and volt, meaning electricity. requires utilities to pay “feed-in In short, the term PV means ficiency in laboratory. tariffs” at fixed premium rates to establish 500 MW of electricity from light. to owners of solar systems for annual capacity and power contributed into grid. 1,000 employees there.

0 1980s 1990s 2000s CONJURING CRYSTAL FROM ROCK

SolarWorld heats and melts poly- CHARGING MELTING silicon rock until The magic starts with about 250 pounds of As the crystal-growing furnace heats up to tem- polysilicon rocks carefully stacked in a quartz peratures ranging around 2,500 degrees Fahren- it forms a white- crucible. The only other ingredient is a silicon heit, its silicon contents melt into a shimmering hot liquid, then disk impregnated with a tiny amount of slurry. Once computerized monitors register the boron. The addition of the boron dopant en- right temperature and atmospheric conditions, re-fuses the mol- sures that the resulting crystal will bear a posi- the alchemy begins. A silicon seed crystal, ten silicon into tive potential electrical orientation. The cruci- hung from a narrow ble is encased within thick walls of insulating cable attached to a a single giant graphite and rotary device crystal in which locked inside atop the a cylindrical furnace, is slowly all atoms are per- furnace. lowered into fectly aligned in a the melt. Polysilicon desired structure Polysilicon rock and orientation. with boron- Seed impregnated silicon disk Quartz crucible Steel furnace encasement enveloping graphite insulation PV POINTER

The method that SolarWorld uses in the United States to grow silicon crystal is known CONJURING CRYSTAL FROM ROCK as “Cz” (pronounced cee-zee). Cz is an abbreviation for the Czochrolski process, named after Polish scientist Jan Czochrolski, who discovered ROWING OOLING the method in 1916 as he re- G C searched crystallization rates The crucible starts to Flash forward about 21/2 of metals. turn, and the seed crystal days since the crucible was begins to rotate in the op- charged with polysilicon: posite direction. The silicon After hours of cooling to melt freezes onto the about 300 degrees Fahr- seed crystal, matching the enheit, the furnace hood seed’s crystalline structure. and shaft lift away from The crystal grows, the the crucible encasement, cable and seed slowly as- slowly swing to one side cend, and the crystal elon- and reveal a completed gates at a controlled cylindrical crystal, ready to width. As the growth move to the second step depletes the silicon and next production room. slurry, the crucible WORD TO KNOW also rises. Crystal measuring Crystal emerging 8 inches wide and 1 A crystal is a solid about 5 /2 feet long Crystal: from melt with molecular building blocks, such as atoms or ions, that have arranged themselves in an identically repeating pattern along all three spatial dimensions. CUTTING WAFERS INTO CELLS

A silicon crystal must change CUTTING SQUARING shape several First, a saw cuts off the crystal’s so-called top Mounted ingots are placed standing on end in a and tail, so that a crystal of uniform width rack bearing 16 at a time inside another wire- times before it remains. Typically, wafering saws draw thin wire slicing machine. There, wire running in a lattice winds up as the bearing a liquid abrasive across the crystal’s configuration descends on the ingots to shear surface. (Below, a machine mounted with a gi- off four rounded segments, leaving flat sides. precisely calibrat- ant donutlike steel blade does the cutting.) Wire The result: The ingots now have a square cross- ed wafers that saws also cut the crystal into ingots measuring section, except for still-rounded corners. 2 feet or less. Steel holders are mounted on the form the founda- ends of these ingots for the next step. tions of photo- Ingots standing on end beneath wire lattice used to voltaic cells. square them Saw wire

Crystal ingot PV POINTER

6” Wafering saws use spools of wire to carry the mineral abra- sive silicon carbide, effectively CUTTING WAFERS INTO CELLS forming a miniscule strand of sandpaper. The spools bear wire measuring about 400 miles long. Stretched out from SolarWorld’s U.S. head- SLICING quarters in Hillsboro, Ore., the wire would reach roughly to The next wire saw is more Helena, Mont. intricate yet. A wire winding hundreds of times between two cylindrical drums forms a web of Helena, parallel, tightly spaced segments. As the Mont. Hillsboro, wire unspools through the machine, Ore. ingots mounted sideways on glass and metal holders are pressed two at a time through the wire web, slicing them into the thickness of slim business cards. Each 1 millimeter of crystal yields about 2 /2 WORDS TO KNOW wafers. Detached from their holders, the wafers are loaded into carriers, or boats, for transport to the Silicon carbide: Silicon carbide next step. (SiC), silicon bonded with Grinding and polishing carbon, is another member of About 100 wafers fit the silicon family of materials steps smooth ingots’ within a transport sides used in the PV industry. It is carrier, or boat a common abrasive in many industries, used in everything from grinding to sandblasting. At SolarWorld, crushed SiC is mixed into a water slurry and applied to saw wires. Silicon carbide, not wire, actually does the cutting.

Saw wire CONVERTING WAFERS INTO CELLS

At this point, a wafer is no more ETCHING DIFFUSING capable of produc- In the only phase requiring a Next, wafers are moved in cartridges into long, cylindrical, oven- ing electricity than designated clean room, a series like chambers in which phosphorus is diffused into a thin layer of intricate chemical and heat of the wafer surface. a sliver of river treatments converts the blank, The molecular-level impregnation occurs as the wafer surface is rock. The wafer is grey wafers into productive, exposed to phosphorus gas at a high heat, a step that gives the blue cells. surface a negative potential electrical orientation. The the main building A so-called texture etch, for in- combination of that layer and the boron-doped layer block of a PV cell, stance, removes a tiny layer of below creates a positive-negative, or P/N, junction – a silicon, relying on the underly- critical partition in the functioning of a PV cell. but so far its only ing crystal structure to reveal notable character- an irregular pattern of pyra- mids. The surface of pyramids – istics are its crystal so small they’re invisible to the structure and naked eye – absorbs more light. positive potential orientation. All of that changes in the third, multi- step, cell-produc- tion phase of PV manufacturing.

Clean suits ensure a sterile Chemical environment bath PV POINTER

Tool: In the PV and semicon- ductor industries, the word tool has a special mean- ing. Instead of referring to CONVERTING WAFERS INTO CELLS an implement that can be applied to a manufacturing mechanism, tools in these fields refer to entire machines or assembly lines that per- COLORING, form a step or series of steps. In both industries, tools are PRINTING highly automated so that The burgeoning, still-grey cells most workers are employed to move in trays into heavy vacuum install, finetune and operate the tools, rather than lifting chambers where blue-purple silicon nitride or moving product. Spider-like is deposited onto their tops. The coating with devices lift and move wafers silicon nitride – yet another member of the silicon and cells on and off conveyor family of materials – is designed to reduce reflection belts for multiple tests along even further in the energy-dense blue end of the light their journey from wafer to cell. spectrum. It leaves the cells with their final, dark color.

Now, the cells can optimally gather photons and pro- duce electricity. They lack, however, any mechanism to collect and forward the power. So, in a series of silk- Drying WORD TO KNOW screen-like steps, metals are printed on both sides of the oven cell, adding pin-stripe “fingers” and bus-bar circuitry.

A functioning cell is born – only sunshine needed. Micron: In cell production, manufacturing steps occur in dimensions measured in microns. In the metric system, Printing a micron is one millionth of a template meter, or one thousandth of a millimeter. For reference, a human hair measures about 100 microns across.

Wafer STRINGING CELLS INTO MODULES

Each phase of pro- duction depends SOLDERING FRAMING on processes with At SolarWorld, module manufacturing is a high- To become a module, however, each laminate ly automated process, relying on robust steel requires not only a frame to provide protec- flavors all their robotics to undertake the increasingly heavy tion against weather and other impacts but own. Careful con- lifting of assembling lightweight PV cells into also a junction box to enable connections modules weighing around 45 pounds apiece. among modules or with an inverter-bound trol of heating and Each robotic tool works within a safety conduit. Robots affix those, too. fence that, by design, excludes people. cooling dominates crystal growing. First, cells are soldered together into strings of 10, using an over-under-over- Wafering employs under pattern of metal connectors to link the cells. Six strings are laid abrasion and cut- out to form a rectangular matrix of 60 ting. Cell produc- cells. Each matrix is laminated onto glass. tion concentrates on chemistry. Any factory process would be incom- plete without a fi- Cell nal assembly step, string and in PV such a step is known as moduling. PV POINTER

SolarWorld is a manufac- turer, not a retailer. It sells Sunmodules mostly through STRINGING CELLS INTO MODULES distributors, integrators and contractors. But the company also sells systems as Sunkits – configurations of modules, inverter and parts that include INSPECTION everything licensed electrical contractors need for specific AND SHIPPING projects at specific locations. Careful cleaning and SolarWorld pioneered this ap- proach in the 1990s. inspection provide final touches before each module can be palletized for delivery WORDS TO KNOW to homes and businesses. Dual channel: SolarWorld uses dual-channel frame tech- nology to provide maximum module strength. Cell-matrix laminants are mounted into frames featuring two metal channels extending all the way around the interior of the frame to encase both sides of the laminate’s perimeter. The resulting module is robust enough to withstand 50 mph hailstone impacts and up to 112 pounds per square foot of wind or snow load. HOW A PV CELL MAKES ELECTRICITY

Under the sun, a photovoltaic cell CELL LAYERS SUN ACTIVATION acts as a photosen- A top, phosphorus-diffused A) Photons bombard and penetrate the cell. sitive diode that silicon layer carries free B) They activate electrons, knocking them loose in both silicon layers. electrons – unanchored C) Some electrons in the bottom layer sling-shot to the top of the cell. instantaneously particles with negative D) These electrons flow into metal contacts as electricity, moving into converts light – charges. A thicker, boron- a circuit throughout a 60-cell module. doped bottom layer E) Electrons flow back into the cell via a solid contact layer at the but not heat – into contains holes, or absences bottom, creating a closed loop or circuit. of electrons, that also electricity. can move freely. In effect, precise manufacturing has instilled an electronic Light-absorbing imbalance between the layer two layers.

N (negative P/N type) junction

Cell cutaway

P (positve type) PV POINTER

It takes all kinds of workers to produce PV, ranging from doctoral engineers trouble- shooting arcane problems to HOW A PV CELL MAKES ELECTRICITY entry-level machine operators learning basic process steps. Within SolarWorld, the four stages of production run as semi-autonomous but inter- POWERING HOMES, BUSINESSES dependent Current leaving a module, or array of modules, passes through a wire conduit leading to an inverter. factories, all with teams This device, about the shape of a waffle iron, inverts direct current, which flows with a fixed current of produc- and voltage, into alternating current, which flows with oscillating current and voltage. Appliances tion engi- worldwide operate on AC. neers, main- tenance From the inverter, the solar-generated power feeds into circuitry of a household, business or power engineers, plant and onto the region’s electrical grid. A remote, or independent, power system also can form a technicians self-contained circuit without connecting to the grid. The off-grid system, however, requires batteries to and operators. store power for times, such as night, when modules do not capture enough light energy from the sun. A Photon

Metal WORDS TO KNOW PV panels contact

Conversion efficiency: This measure gauges the percent- age of solar (light) power reaching a module that is con- C D Inverter verted into electrical power. Conventional cells now range in the high percentage teens. Theoretical and laboratory Electron conversion rates typically are B Fuse box much higher than rates from mass production.

Metal back TV

E Electrical grid YOU ENTER THE EQUATION

PV technology is largely a U.S. SOLAR ENERGY’S FUTURE original. But Grid parity – the point where installing a PV system foreign ingenu- becomes less expensive than buying fossil-fuel energy ity has grasped – is the goal of the solar industry. its leadership by Thanks to two centuries of increasingly intensive use, fossil fuels have reached economies of scale that en- applying mar- able very low unit prices but cause enormous environ- ket mechanisms mental harms. that jumpstart Various government and nonprofit agencies are of- fering an array of incentives to help accelerate the PV higher investment industry’s growth and the unit-cost reductions that returns. Creating large-scale manufacturing brings. higher demand, SolarWorld Sunmodules have already reached these policies build grid parity in a few locations where ample sunshine is combined with high prices for economies of scale fossil-fuel energy. Available that force down incentives are helping them to close the gap everywhere else. pricing. But it takes people – you – to make choices for a better planet. Now the U.S. is reawakening to the promise of solar energy. PV POINTER

So how much power does a typical PV system produce – and at what cost? A modest YOU ENTER THE EQUATION rooftop system for a home might combine 1.5-3 kW in modules and produce the equivalent of about one-third of the home’s power needs. In SOLAR MARKET INCENTIVES some locations, the ultimate costs to the system owners Dozens of countries have imple- Incentives vary among nations, states and even Feed-in tariffs: – figuring in all incentives – cities, but they typically fall into these catego- mented feed-in tariff systems – set premium might amount to 30 cents ries: rates that utilities are required to pay for power on the dollar. In that case, a from solar systems. The rates remain fixed for hypothetical system priced Rebates: Some organizations distribute outright a set number of years, perhaps 20. A power at $25,000 actually would reimbursements for a portion of system costs. producer, such as a homeowner or business, cost about $7,500. Returns Tax incentives: The U.S. government and sev- on investment in many cases separately pays normal market rates for power exceed average typical interest eral states may offer investment tax credits or from the grid. on certificates of deposit. accounting provisions allowing extraordinary terms for asset depreciation. On Jan. 1, 2009, for Falling solar prices will cross rising prices instance, the federal government removed a of fossil fuels $2,000 cap on a 30 percent credit for residential With government incentives, then without, WORD TO KNOW systems. rising solar demand and falling unit pricing are leading to grid parity. Net metering: This alternative to feed-in tariffs allows solar power producers to generate and Fossil fuels Insolation: Sunlight varies by use power at the same price rates and accord- region. Insolation is a measure ing to a single meter. When a home system, for Solar of the solar radiation energy instance, makes more power than it uses, its in a given region. It is usually meter rolls backward. Solar with expressed as the intensity of Price per watt incentives light energy per unit of land area. As a whole, the U.S., Time especially the sunny South- west and Southeast, offers strong insolation. By comparison, Germany, the PV industry’s leader, gets little better sun than Alaska. BEYOND ROOFTOPS

These days, PV technology is ANYWHERE THERE’S SKY extending beyond While rooftop systems provide countless homes and businesses with power right where they most rooftops into need it, such installations are far from the only kinds of PV projects harnessing photons. locations that have Ground-mounted Canopy systems can Utility-scale systems Tracker systems in- systems make sense provide shelter and come in a variety of crease their output never known the where roofs are una- produce power in park- dimensions, but all pro- power by moving to benefits of elec- vailable or inadequate. ing lots and exterior duce enough electricity follow the sun’s Modules are mounted corridors. to power many path. tricity. As on-grid on racks anchored into buildings. applications bring the ground. cleaner power to wired homes, so, too, do off-grid systems empower those without elec- tric refrigeration and lighting. Along the way, SolarWorld has led the world industry in rural electrification and sustainable prac- tices. “Sustainable development is BEYOND ROOFTOPS designed to lead to a situation where present RECYCLING, REUSING THE VISION generations can SolarWorld has led the global PV industry in ap- SolarWorld’s Solar2World program takes aim at satisfy their own plying principles of sustainability. the 2 billion people on the planet who go with- out electricity, a number that promises to rise needs without Internally, SolarWorld uses residual and rem- with population growth. Working with nant silicon left in crucible bottoms or cut from jeopardizing the local partners, the company donates its modules ingots to reform crystal, and it strives in every into rural electrification projects in some of the potential needs imaginable direction to divert waste leaving its world’s poorest areas. With operations – plastic packaging, spent wire, even of future SolarWorld’s coffee cups – into second or new uses. expansion in the generations.” Externally, SolarWorld long has operated the United States, world’s only crystalline photovoltaic recycling the Solar2World Frank H. Asbeck plant. The operation at SolarWorld’s site in program there SolarWorld chairman and CEO Freiberg, Germany, disassembles and proc- focuses on esses modules not only for the company but Latin also for member companies of PV Cycle, a America. consortium of European PV manufacturers spawned by SolarWorld. + =

l Largest U.S. manufacturer of crystalline photovoltaic technology l Among oldest U.S. manufacturers, dating to modern industry’s mid-1970s dawn l One of world’s biggest PV manufacturers, with operations in every major market l Repeat leader in Photon International magazine’s annual performance test of modules l Parent company headquarters in Bonn, Germany; U.S. headquarters in Hillsboro, Ore. l U.S. sales offices in Camarillo, Calif., and Boca Raton, Fla.

Main sales office Headquarters 4650 Adohr Lane 25300 N.W. Evergreen Road Camarillo, CA 93012 Hillsboro, OR 97124 +1-805-388-6200 +1-503-844-3400

SolarWorld. And EveryDay is a SunDay www.solarworld-usa.com